Solvent dewaxing of lubricating oil distillates results in the occurrence of large quantities of slack wax. Slack wax is a mixture containing isoparaffins, normal paraffins and also lower melting point constituents usually referred to as oils and naphthenic constituents. The slack wax may contain from about 5-25% of oil as determined by ASTM test No. D 721.
For many years it has been known that the oil content of some oil-containing waxes may be reduced by resort to the so-called sweating process. This, essentially, involves providing a mass of the oil-containing wax at a temperature sufficiently low for it to be solid and then very gradually raising the temperature of the solidified mass whereby the components of lower melting point will tend to become liquefied and drain away at least in part from the higher melting point wax. While there have been various proposed procedures for accomplishing sweating, it has been recognized that sweating, at least as heretofore practiced, is very inefficient and time-consuming. The time required for processing a given stock completely may vary from several days to as long as several weeks. The wax sweating as heretofore carried out also is inefficient in that the separation of the oil and other lower melting point constituents is far from complete, with the result that in order to reduce the oil content of the hard wax to desired specifications it is not unusual to employ several successive sweating operations. The disadvantages incident to sweating as a method for reducing the amount of low melting point constituents in a wax composition such as slack wax has led the industry to place reliance for the most part on the solvent extraction procedure wherein a wax such as slack wax is dissolved in a solvent such as methylethylketone (or methylisobutylketone) followed by chilling the solution to cause precipitation of the desired portion of the wax which is filtered out using a rotary vacuum filter. For most purposes solvent extraction does not reduce the oil content of the wax to a sufficient extent in one stage and the wax-rich product resulting from the initial extraction is reslurried at least once with additional solvent followed by cooling and subsequent filtration. By two or more successive operations the resulting product is expected to contain less than 1% of oil. As compared with the equipment required for this invention, the equipment for solvent extraction requires a very substantially greater capital investment. Moreover, the equipment used for solvent extraction as a matter of economics does not lend itself to the economic construction of processing equipment for small-scale operation.
It is apparent from the foregoing there has been a recognized need for a deoiling procedure applicable to slack wax or the like which would be comparable in effectiveness to the solvent extraction procedure but which could be installed and placed in operation at much less expense and which lends itself not only to large-scale operations but also to scaled-down operations.